1. Field of the Invention
This invention relates to battery protection circuits and more particularly to circuits for preventing any cell of a battery from being forced into reversal.
2. Description of the Prior Art
Some cells of a multi-celled battery can be driven into cell reversal during discharge. When forced into reversal, high energy density cells such as lithium/sulphur dioxide cells can and do vent violently with the possibility of the cell case rupturing explosively causing a fire hazard and the release of noxious gases such as sulphur dioxide and acetonitrite.
Some of the present lithium/sulphur dioxide batteries use silicon diodes connected around each cell to prevent the cells from reversing more than 0.8 Vdc. That is, if the cell voltage falls below zero volts, the diode will short circuit the cell at a voltage around-0.8 Vdc. However, it has been shown that this voltage clamp does not guarantee that any one cell will not vent violently when reversed.
It is possible that the change in chemical composition as the cell potential falls below zero volts may be sufficient to create an unstable cell.